From: Tord Romstad <tord@glaurungchess.com>
Date: Mon, 5 Oct 2009 14:46:18 +0000 (+0200)
Subject: Fixed an embarassing Chess960 bug found by Alexander Schmidt.
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=32dfaa56b03fda5ecd72f11b36130aa25b556ae9;hp=3701a8e57ded0876bd34ba1bc1afafc631ee059b

Fixed an embarassing Chess960 bug found by Alexander Schmidt.

It turned out that we used do_move_bb to update the king and rook
bitboards when making and unmaking castling moves, which obviously
doesn't work in Chess960, where the source and destination squares
for the king or rook could be identical.

No functional change in normal chess.
---

diff --git a/src/position.cpp b/src/position.cpp
index 00503429..e0e9aa3a 100644
--- a/src/position.cpp
+++ b/src/position.cpp
@@ -985,17 +985,22 @@ void Position::do_castle_move(Move m) {
       rto = relative_square(us, SQ_D1);
   }
 
-  // Move the pieces
-  Bitboard kmove_bb = make_move_bb(kfrom, kto);
-  do_move_bb(&(byColorBB[us]), kmove_bb);
-  do_move_bb(&(byTypeBB[KING]), kmove_bb);
-  do_move_bb(&(byTypeBB[0]), kmove_bb); // HACK: byTypeBB[0] == occupied squares
-
-  Bitboard rmove_bb = make_move_bb(rfrom, rto);
-  do_move_bb(&(byColorBB[us]), rmove_bb);
-  do_move_bb(&(byTypeBB[ROOK]), rmove_bb);
-  do_move_bb(&(byTypeBB[0]), rmove_bb); // HACK: byTypeBB[0] == occupied squares
-
+  // Remove pieces from source squares:
+  clear_bit(&(byColorBB[us]), kfrom);
+  clear_bit(&(byTypeBB[KING]), kfrom);
+  clear_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
+  clear_bit(&(byColorBB[us]), rfrom);
+  clear_bit(&(byTypeBB[ROOK]), rfrom);
+  clear_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
+
+  // Put pieces on destination squares:
+  set_bit(&(byColorBB[us]), kto);
+  set_bit(&(byTypeBB[KING]), kto);
+  set_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
+  set_bit(&(byColorBB[us]), rto);
+  set_bit(&(byTypeBB[ROOK]), rto);
+  set_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
+  
   // Update board array
   Piece king = piece_of_color_and_type(us, KING);
   Piece rook = piece_of_color_and_type(us, ROOK);
@@ -1106,6 +1111,7 @@ void Position::undo_move(Move m) {
       pieceList[us][PAWN][index[to]] = to;
   }
 
+
   // Put the piece back at the source square
   Bitboard move_bb = make_move_bb(to, from);
   do_move_bb(&(byColorBB[us]), move_bb);
@@ -1183,17 +1189,22 @@ void Position::undo_castle_move(Move m) {
 
   assert(piece_on(kto) == piece_of_color_and_type(us, KING));
   assert(piece_on(rto) == piece_of_color_and_type(us, ROOK));
-
-  // Put the pieces back at the source square
-  Bitboard kmove_bb = make_move_bb(kto, kfrom);
-  do_move_bb(&(byColorBB[us]), kmove_bb);
-  do_move_bb(&(byTypeBB[KING]), kmove_bb);
-  do_move_bb(&(byTypeBB[0]), kmove_bb); // HACK: byTypeBB[0] == occupied squares
-
-  Bitboard rmove_bb = make_move_bb(rto, rfrom);
-  do_move_bb(&(byColorBB[us]), rmove_bb);
-  do_move_bb(&(byTypeBB[ROOK]), rmove_bb);
-  do_move_bb(&(byTypeBB[0]), rmove_bb); // HACK: byTypeBB[0] == occupied squares
+  
+  // Remove pieces from destination squares:
+  clear_bit(&(byColorBB[us]), kto);
+  clear_bit(&(byTypeBB[KING]), kto);
+  clear_bit(&(byTypeBB[0]), kto); // HACK: byTypeBB[0] == occupied squares
+  clear_bit(&(byColorBB[us]), rto);
+  clear_bit(&(byTypeBB[ROOK]), rto);
+  clear_bit(&(byTypeBB[0]), rto); // HACK: byTypeBB[0] == occupied squares
+ 
+  // Put pieces on source squares:
+  set_bit(&(byColorBB[us]), kfrom);
+  set_bit(&(byTypeBB[KING]), kfrom);
+  set_bit(&(byTypeBB[0]), kfrom); // HACK: byTypeBB[0] == occupied squares
+  set_bit(&(byColorBB[us]), rfrom);
+  set_bit(&(byTypeBB[ROOK]), rfrom);
+  set_bit(&(byTypeBB[0]), rfrom); // HACK: byTypeBB[0] == occupied squares
 
   // Update board
   board[rto] = board[kto] = EMPTY;